The Sunscreen Mistake You're Probably Making

You know how Alexander Fleming discovered penicillin by accident and it was hailed as a medical miracle? Well, this isn't that, but I think I discovered something important about sunscreen.

It all started because my kids like juice boxes. But not warm juice boxes. (They're kids, not idiots. Warm juice is disgusting.) That's why I carry an insulated tote to the beach. Everything goes in it: snacks, keys, Kindle, sunscreen, and 45-degree juice.

But last weekend, I left the bag in the car and forgot about it until the next day. When I discovered it baking in the backseat, my brain went straight into beauty-editor mode: Is my sunscreen totally useless now? Excessive heat renders sunscreen ingredients less potent (at best) or inactive (at worst). In other words, major sunburn risk.

But since the neglected sunscreen had been in an insulated bag, it felt nice and cool. Did that mean it was OK? Rather than toss out a brand-new $30 bottle, I hit up some experts for advice. "I never really thought about keeping your sunscreen in an insulated compartment before," said New York City–based dermatologist Joshua Zeichner. "Yes, you should definitely do that if your sunscreen is going to be out in the sun. Good idea."

That was encouraging. Next I spoke to Mona Gohara, an associate clinical professor of dermatology at Yale. "Keeping your sunscreen cool definitely helps!" she said. "Good idea. I'm sharing it with all my patients."

So if you're heading to the beach, taking a road trip, or hanging out by a pool all day, stash your sunscreen in cooler bag (just don't throw any ice in there— extreme temperatures are a bad idea). It will protect and preserve those essential filters and reduce your risk of a burn.